1. Field of the Invention
The present invention relates to a receiver apparatus which receives substantially concurrently a plurality of signals that have been transmitted while being allocated in a broad band, and uses the received signals.
Therefore, the present invention can be used in various applications, such as RoF (Radio on Fiber) and radio units at base stations, which receive signals of a plurality of channels concurrently.
2. Description of the Related Art
FIGS. 26 to 29 are block diagrams showing the overall configurations of conventional receiver apparatuses (Conventional Examples 1 to 4). In these drawings, reference letter N represents the “number of providable media,” and M represents the “number of signals which can be processed simultaneously.”
Conventional Example 1 (FIG. 26)
<Processing Bands/Processing Scheme>
                (a) Channel extraction: RF band→IF band        (b) Sampling: Base band        (c) Orthogonal demodulation: analog<Features>        
An anti-aliasing filter is used. Selection of each channel is performed in the IF band (analog).
Conventional Example 2 (FIG. 27)
<Processing Bands/Processing Scheme>
                (a) Channel extraction: IF band (RF band)→Base band        (b) Sampling: Base band        (c) Orthogonal demodulation: analog<Features>        
Since reception signals are monitored in an analog section by means of, for example, channel scan (media scan), a hardware switch mechanism is provided. A direct conversion scheme in which extraction of each channel is performed in the base band (analog) is employed.
Conventional Example 3 (FIG. 28)
<Processing Bands/Processing Scheme>
                (a) Channel extraction: RF band→IF band        (b) Sampling: IF band        (c) Orthogonal demodulation: digital<Features>        
A switch is used. Channel extraction is performed in the base band (digital).
Conventional Example 4 (FIG. 29)
<Processing Bands/Processing Scheme>
                (a) Channel extraction: IF band (RF band)→Base band        (b) Sampling: IF band (RF band)        (c) Orthogonal demodulation: digital<Features>        
A switch is used. Channel extraction is performed in the IF band (analog).
Relevant techniques relating to these conventional techniques are disclosed in, for example, “Multimedia Wireless Transmission System Using Complex-Coefficient Multirate Filter Bank,” IEICE transactions, B-I Vol. J81-B-1 No. 11, pp. 671–680, November 1998; “Application of Multirate Filter Bank to Group Demodulation of Frequency-Multiplexed TDMA Signals,” IEICE transactions, B Vol. J83-B No. 9, pp. 1217–1225, September 2000; and “Development of Software Radio Apparatus for ITS Capable of Simultaneous Communications,” Proceedings of the 2001 IEICE General Conference, A-17-45, pp. 426.
In order to increase flexibility (versatility) of signal processing to thereby cope with multimedia of a wide range of types, a larger part of signal processing as compared with conventional techniques must be realized by means of digital signal processing (software). However, simple replacement of a conventional technique with digital signal processing (software) results in a great increase in computational complexity imposed on a digital signal processing section, thereby rendering difficult enhancing flexibility and practicability of such signal processing.
Specifically, conventional techniques involve the following problems.
Problem 1:
In the case in which sampling is performed in the IF band, at least orthogonal demodulation must be performed by means of digital signal processing, thereby increasing the computational complexity for digital signal processing.
Problem 2:
In the case in which analog orthogonal demodulation is performed, the configuration can be simplified through employment of direct conversion; however, adverse effects may be caused by the orthogonality or the DC component.
Problem 3:
When concurrent processing of a plurality of services is desired, the scale of hardware must be increased.
Problem 4:
Since services (media signals) to be processed concurrently cannot be selected in advance, during periods for awaiting input signals, the analog section must perform channel scan (media scan).